Inkjet printing systems typically include one or more print units, and each print unit has one or more printheads. A controller controls the printhead to eject a fluid (such as ink or another composition) onto a medium. Each printhead includes a nozzle plate that includes a plurality of orifices (nozzles) through which ink from inside the printhead may be controllably ejected.
A printhead typically includes a fluid chamber in fluid communication with one or more of the nozzles. Pressure inside of the fluid chamber is increased relative to ambient air pressure to force a drop of fluid through the nozzle(s). One type of printhead uses a piezoelectric element that deforms a wall of the fluid chamber to reduce the volume thereof and thereby increase the pressure within the fluid chamber. Alternately, a heating element may be used to vaporize some of the fluid (or a constituent of the fluid such as a fluid carrier or a solvent) in the fluid chamber to form a bubble therein, which increases the pressure inside the fluid chamber. In either case a controller controls the current that is passed through the piezoelectric element to control the deformation thereof or controls the current through the heating element in turn to control the temperature thereof so that drops are formed when needed. Other types of inkjet technologies known in the art may be used in the printing systems described herein.
In a printing system, the printhead is secured to a mount and disposed such that the nozzles of the printhead are directed toward the medium. In some embodiments, more than one printhead may be secured to the mount in a one- or two-dimensional array. Further, some printing systems may include a plurality of mounts, wherein each mount has one or more printheads disposed therein in a one- or two-dimensional array. In such systems, the plurality of mounts may be disposed in the printing system in a one or two-dimensional array and the nozzles of the printheads in these mounts are directed toward the medium.
Dried ink, dust, paper fibers, and other debris can collect on a nozzle plate or in one or more nozzles of the printhead and prevent proper ejection of ink from such nozzles. The controller of a printing system can undertake periodic cleaning cycles during which ink is purged from the nozzle(s) to release any debris in or near such nozzle(s). The purged ink and/or debris must be removed from the nozzle plate in the vicinity of the nozzles, for example, by wiping, so that such purged ink and/or debris does not collect on the nozzle plate and dry to create further debris that will later interfere with ejection of ink from nozzles of the printhead.